The impeller has been replaced, engine was rebuilt with new water pump because the original engine had overheated too. The boat owner didn't replace the impeller until after the rebuild. At mid to high speeds the water temp stays below 160. At low speeds the temp will rise over 200 unless the operator speeds up to cool it down. The original exhaust manifold is still being used. Any suggestions? Thanks in advance.

rjinmt

06-05-2010, 01:39 PM

check to see if any debri is in inlet line from impeller up. strart simple first!

Ok, thanks. Do these exhaust manifolds ever crack from overheating? Or are they pretty "bullet proof"?

chiefalen

06-06-2010, 10:52 AM

maybe and the head gasket can go also, Take the hose off the t-stat housing the long one from the transom, put water to the drive and start the boat hold the hose straight up you should have 12-15 inchs of water. 3-4 seconds is all you need quick shut off the motor.

Going to lake to test now,will give you report. Garden hose would "force feed" so I will idle for a moment at the dock and test impeller output there. Have been swamped with work, wish I could concentrate on one thing at once. I'm primarily an outboard and automotive repair, but doing this job for a friend who has been frustrated with it. Thanks so much, Tim

chiefalen

06-09-2010, 09:54 AM

have a problem post back, may the force be with you.

guido2

06-09-2010, 03:03 PM

Ok, idled @ dock and raced up to 180. Put in reverse and worse. Won't overheat with slow foreward.....go figure. Checked output and pretty low. At idle about a slow garden hose flow. Figured bad pump so back home and took apart. Owner had replaced impeller but housing was a bit melted by the stainless steel insert. Also noticed a bit warped where it seats on baseplate. Blew back through supply line with air and great flow. Also blew down from pump inlet and had good flow of air out water intake screens. My guess is a bad pump housing and replace impeller again. Seems the stainless steel pump housing insert is distorted too. Impeller has suffered some already. What do you think? Thanks, Tim

chiefalen

06-09-2010, 04:10 PM

Listen make believe i just slapped you lightly on the back of the head. The impeller was all busted up at one time? If yes i bet it was cause the impeller housing was melted. It was melted cause someone ran the drive with no water going to it. Capiche?

Sooo look for the pieces ! Take the hose off the transom the pieces could be clogging that hose or fitting on the other side of the transom.

No pieces there then they might be in a heat exchanger if you got one follow the hose.

T-stat housing overflow hole might be clogged up. not clogged up or the t-stat if clogged up or frozen clossed or something.

Then follow the thought here, Take the hoses off the engine mounted circulating pump. Only other small holes are in the riser.. If not finding no pieces then ya gotta take off the riser, it good ? Clogged up or fugazied ?

Say that it's good then stick ya face down the tube could be a flapper / shutter fell down or melted off and is blocking the exhaust.

Make believe i'm waving both hands at you, go find the clog, and post back.

Good luck keep us posted if you get in a jam, and or fix it .

guido2

06-10-2010, 08:28 AM

Thanks.....so to avoid another head slap, I'd better not only replace the pump but find the blockage. Ok I'll look closer. Seems as soon as you give the motor a little rev, it will pump water.....otherwise low output.

The link worked great.....the kit is on its way from Iowa. Thanks, Tim

chiefalen

06-10-2010, 02:40 PM

Good luck !

guido2

06-16-2010, 02:26 PM

Ok, new kit installed and pre lubed with lite synthetic oil. Tested at dock with output hose off at thermostat housing. Result, no water flow at all. What the h_ _ _ did I do now?

guido2

06-16-2010, 02:37 PM

Is the little crack in output side hose a problem? Whats happening here? Had low water flow before, now nothing. Checked for any blockages or leaks but all ok.

guido2

06-16-2010, 02:40 PM

Hey "Chief", you can kick me now.

chiefalen

06-16-2010, 03:18 PM

The hose kinked at the transom inside? I'm bing nice today so no kick. Try putting water backwards down the long hose from the t-stat back cobble together the garden hose and the motor hose, and see what water comes out the back.

Jeez your getting a bum rap wit this chittt.

guido2

06-17-2010, 09:53 AM

Thanks, great water flow both ways and when water is applied to the motor imput, it comes out under stern drive unit at base of transom. No thermostat, the owner took it out.

guido2

06-17-2010, 01:40 PM

In my third photo you see the hole in the little hose. Is that just a pressure relief hose when the thermostat is fully closed? C'mon techs......this guy has been fighting this overheating problem for 2 years and its desroyed one 3 litre motor already. HELP!

boatin_bob

06-17-2010, 05:07 PM

When you put the water pump kit in did you replace the impeller again? The reason I ask is because there are questionable ones out there. Last year I went through 4 impellers on my twins, one brand new one in the spring quit working the following weekend the other stopped working mid-summer. Yet when you pull them they look brand new? Anyway just a thought if you still have the other new one to swap them.

chiefalen

06-17-2010, 05:15 PM

Jeez i wish i could touch it . You think the water is pushing or sucking thru the slit huh? How much could that f--king thing be ?

Got a dealer near you ?

I mean if everything else is good ...

guido2

06-18-2010, 12:22 AM

I used the new impeller that came with the kit. I could try the old one and use it in the new housing to see what happens. The old impeller does seem more flexible.
To "Chief" I say no I'm not too worried about the little slit in the relief hose, but this boat has the best dealer in northern Minnesota puzzled too. The owner has put thousands into this problem already. Hell, I should be able to figure it out with a little help from "my friends". You want me to go at it on my own?

chiefalen

06-18-2010, 04:46 AM

No i'll never give up if you don't. Theres a crack somewhere. Some how you can't see it.

It's the only thing left.

the_tassie_devil

06-18-2010, 07:49 AM

The split in the tube in the third picture, is that the pressure hose?

The reason I think it is getting enough water to cool the engine at speed is that the prop is forcing the water into the inlet, and the engine's own water pump is turning sufficiently fast enough to suck the necessary coolant past the split in the pipe, and into the engine.

That split is way too big to allow sufficient flow to go through the hose, unless there is the vacuum from the Water Pump upstream to assist.

Bruce.

PS. I may be wrong, but I love pictures.

PPS. I don't even know what a Cobra looks like, the marine version that is, so you can tell me to shut up if you like.

chiefalen

06-18-2010, 11:01 AM

Taz alot like a alpha.

That hose got to go like a posted how mush is that f--king hose. Actually i got so many stikin size hoses i would have cut one to fit.

And if i didn't have it my friends got all kinda size rubber hose, i would have went over and cut a piece.

guido2

06-18-2010, 11:14 AM

Ok, the split is in a tiny hose venting from the output lobe on the water pump. The little hose terminates in the lower housing thus venting a small amount of the pumps output back to the lake. For the "Devil" don't be afraid to give advice, I appreciate any I can get. Sometimes even poor advice can spark a solution.
I did check pressure between water pump outlet and thermostat housing and there are no leaks on the output side.
There has to be a solution. Hell, we put a man on the moon..........didn't we?

guido2

06-19-2010, 08:59 AM

Also I hooked water supply from house to engine intake at thermostat housing and it cools perfectly. Could there be a problem with pump rotation direction?

boatin_bob

06-19-2010, 09:22 AM

Looking at your pic above with the impeller inside the housing you've got it in the right way and it should turn CCW, have you changed the impeller again yet? Also (dumb question) but are you absolutely sure that the water pump shaft is turning? Very rare but have heard of the shaft breaking inside, everything still works fine except for the water pump. If all else has failed I would be removing the drive and separating the halves to inspect the entire water passage area.

http://i108.photobucket.com/albums/n15/thun5der/cobra.jpg

the_tassie_devil

06-19-2010, 08:27 PM

Heck, I don't even know what an Alpha looks like, but I do know that a hose with a hole in it is not good.

You would be surprised just how much liquid will try to escape through the opening with the lease resistance, and a split that large is going to leak a LOT.

Bruce.

PS. I love pictures and diagrams.

PPS. I knew nothing about Stern Drives until I got my own in 2008, and I had to get the one with the least available parts. My previous dealings was with fitting big stuff like Gardiner 8LX and 8LW's into timber fishing boats with 3" prop shafts.

guido2

06-20-2010, 10:09 AM

Thanks for the response. No, I have not tried the old impeller yet into the new housing. I don't think thats the problem. When I crank the motor with my remote switch I get CCW rotation on pump drive shaft. You can see the wear mark on the shaft where the impeller has been pushed during its rotation over time. When I ran the motor at the dock it was submerged in the water while still on the trailer. So the water level was right level with the pump. So if there was a leak on the suction side say near the water tube, it would have been underwater anyway. Still the pump output is very very poor, like about 3 or 4 gallons per minute at idle.......that is measured at thermostat inlet hose coming up directly from pump. Any more suggestions? Thanks, Tim

guido2

06-20-2010, 10:18 AM

So then what does the little tube with the hole/split in it do? I don't think it is critical.

chiefalen

06-20-2010, 11:47 AM

Listen, are you listening ? Smack in da back of da head again ! Jeez ya worse then my 18 year old son.

THERE IS A CRACK SOMEWHERE ! Might be the water pump housing, might be a o-ring, might be the tube that the water pump tube slips into, might be a hose.

Capiche ? Find the motherf--king crack don't over look the base water flow it opens under pressure, close off the water flow and you don't see it cause it looks good cause it closed back up.

Same on cracks on blocks and mani's, risers.

You might have to pressure test the water pump system and see if it holds say 15 psi for a hour. That you got to do on the bench.

Don't give up, don't give in, i got confidence in you ! Do what you got to do find the problem fix it and move on. Keep your chin up !

boatin_bob

06-20-2010, 07:43 PM

Thanks for the response. No, I have not tried the old impeller yet into the new housing. I don't think thats the problem. When I crank the motor with my remote switch I get CCW rotation on pump drive shaft. You can see the wear mark on the shaft where the impeller has been pushed during its rotation over time. When I ran the motor at the dock it was submerged in the water while still on the trailer. So the water level was right level with the pump. So if there was a leak on the suction side say near the water tube, it would have been underwater anyway. Still the pump output is very very poor, like about 3 or 4 gallons per minute at idle.......that is measured at thermostat inlet hose coming up directly from pump. Any more suggestions? Thanks, Tim

OK so you do have some water flow at idle, I thought you had none. The Cobra does not pump water like the old stringer 800 so with the input hose off at the t-stat housing at idle you should 2-4" of a head, if you do then your problem is downstream from there.

guido2

06-21-2010, 09:31 AM

Thanks, I don't see the answers I gave you yesterday so I will post again.
I didn't try the old impeller again yet....its not my suspect. When I try at the dock with the boat still on trailer, the water pump itself is at water level. Wouldn't you think that the water tube housing would be full and any suction leaks would inhale water anyway? What function exactly does the little hose perform in my photo with the split in it? I bought a large livestock tub so I won't have to keep running to the landing now to test it. I don't see any check valves on the suction side either, why not? Thanks, Tim

guido2

06-21-2010, 09:40 AM

Ok, I see my old post. I must say that the water supply from pump is not consistant. Sometimes you get water, sometimes you don't. My testing thusfar has been with the outdrive deeply submerged at the dock. If you idle the motor in reverse it seems to overheat faster than in forward. The boat owner simply cannot troll or idle without heat climbing. When I run the garden water hose into the thermo housing I get tremendous and uninterupted water flow out base of stern drive at transom. Is that correct scenario?

boatin_bob

06-21-2010, 12:32 PM

I know my own Cobra's needed to be submerged right up to the top of the drive so the pump was more or less under the water. The small hose is just a vent/drain line, I think I've seen some guys run without one. I think your at the point where you have to remove the drive and split the upper/lower.

the_tassie_devil

06-21-2010, 06:58 PM

The Owners Manual recommends that one doesn't run in reverse, or go astern for long periods, or at higher speeds, as the action of the Prop takes water away from the intake point.

When forward gear is selected, the prop is actually pushing water in the direction of the intake.

Bruce.

guido2

06-22-2010, 10:22 AM

Yeah, thanks guys. Seems I always get these nasty jobs. I suppose the intake ports are engineered to accept water most effectively when traveling forward. What could possibly be askew inside the housing? There is most certainly no restriction when I send water or air down from the intake opening with the pump off. Secondly if there was an opening somewhere sucking from above the intake screens, that area is completely submerged while I'm testing......therefore I should still get adequate water delivery at the engine intake. What is your idea or what have you seen that goes wrong inside the housings? Thanks, Tim

guido2

06-23-2010, 09:24 AM

Hey Chief, you sound just like my dad.......ha! Believe it or not, he was my hero. He could figure out anything. He would smack you on the head, then if that didn't do it he would get out the "black wooden stick". Ha! By then you were perfectly good and listening to your next order. He was a 1st Lieutenant in WWII infantry. Italian 100 percent. He was right almost all the time.
Bob, guess I'll have to tear more into it and look for problems on the suction side.
Bruce, thanks for the imput and I'll post what I find. The boat owner is getting pissed but I have 10 other jobs I'm doing at the same time. I'm just trying to pay the bills here and so we can survive. Have only been able to get up to our Ontario cabin once in the last year.

boatin_bob

06-23-2010, 12:06 PM

I don't think you have anything between the transom and the t-stat in the input line such as a power steering cooler or an oil cooler (I had both on mine) so unless there's a chunk of old impeller lodged in the upper water tube (going through the transom) I think your problem is below the pump....good luck !!!

guido2

06-24-2010, 09:37 AM

Thanks Bob, the water tube is clear and no leaks. It runs direct with no other devices in line. I will try to pressurize the intake side first, before I dismantle. Maybe I will detect a defect or leak within the housing. If I plug the pump inlet and apply water with the muffs, perhaps I may find something wrong.

Another question. Does the water intake passage tube that comes up from the intake screens pass through an area that could collect air from the exhaust? Then if thats the case the chamber could introduce air to the suction side of the pump even though it is fully submerged. What do you think folks? Thanks....Tim

chiefalen

06-27-2010, 11:51 AM

Nope if submerged however if the fitting that passes thru the transom has a crack or the hose has a crack on the inside of the transom then air can be sucked in.

The hose under the clamp can be cracked. Can the hose itself be kinked near the transom?

Capiche ?

guido2

06-30-2010, 10:00 AM

Ok, I checked the intake side by putting water pressure with the "muffs" and plugging the intake opening with the water pump removed.........(see old photo of pump). What I find is not only seepage out weep holes in front of intake screen but discharge out area near anode. What do you think.......??? Supposed to be?

wes77

06-30-2010, 12:35 PM

Do you know what the water pump rating is for gpm at the idle rpm? seems to me 3-4 gpm is pretty good for a little impeller running at idle.

Have you checked your exhaust flapper? I have an 89 OMC 3.0l cobra and mine was binding even though it looks like new. It didn't seem to affect engine operation or performance, but I would get water in my engine oil because it wasn't closing when backing up. I would assume it could also cause overheating if it was closed or partially closed at idle and pushed open more when the exhaust pressures rise with RPM... maybe not the problem, but might be worth a look. just slide the rubber boot that links your riser to the down dube downward to expose it and check operation with your finger.

The bushings on either side are rubber and the flapper is rubber coated. the bushings were causing my flapper to bind and not move freely. I just replaced th bushings with nylon flange bearings last night. I have to test it out yet, but I think it will work well. Operation is now free and easy, like a float.

also, seems to me if you are loosing so much water at idle you can't cool it, you would have similar problems at high rpm. It might move more water at higher rpms, but where is it all going? cracks in blocks and manifolds will put water in your oil. if your oil is clear and your engine runs fine, I would look elsewhere. You have darn near replaced everything. Unless all of your new parts are bad or unless you do have some intermittent obstruction, I'm guessing your problem is elsewhere.

I could be wrong, but the flapper is worth a look. takes 5 mintes to slide the boot down and check.

guido2

06-30-2010, 01:47 PM

Thanks for the response. The pump will not provide water to the thermostat all the time. If you get the water pumping in forward gear while submerged at the dock, then it will pump about 3 gallon per minute. If you stop and then restart the motor at slow idle or reverse, it will not pump at all. In other words no water supply to the motor. The customer has taken the boat back but will return after the holiday weekend. He knows how to keep the temp down by watching the temp. guage and adjusting his forward boat speed if it starts to heat up. Its been doing this for 2 years but he wants to fix it as he can't idle or run for prolonged time at low speed. He is an avid waterskier. So whatever is the problem.....its consistant.
No I have not checked the flapper as I do know that it is a supply issue from the outdrive water pump. Thanks, Tim

guido2

06-30-2010, 01:50 PM

Remember now that this motor will not overheat when water is fed directly to the thermostat housing inlet from the garden hose.

wes77

06-30-2010, 03:33 PM

Ok, sounds like you have it narrowed down.

If it is intermittent, are there missing teeth on the drive gear for the impeller? I would assume it is driven off of the crank or cam. Is it belt driven externally? or internally? I should know this as I have an 89, but I haven't had issues with it so don't recall. If there are missing or worn teeth, it could mesh some times, then hit a bare spot and stall out. You mentioned it moved when you turned it over, but did you apply a load? it might turn, but when it is placed under load, the drive end slips. For that matter, if it is driven externally, any chance there is belt slippage? That would likely be very noticeable, but again, just throwing it out there.

You wouldn't think forward or reverse would matter as the water pump should be driven in the same direction with the engine all the time. any chance there is debris that falls out of the way in one direction, then gets pulled back into obstruction in another (in a passageway that is open to the effects of boat motion)? not sure if this is likely or even possible, but an idea.

Regarding leaks, any chance you could introduce smoke of some sort into the passageways and look for leaks that way? they do that where I work to look for leaks in pressurized cabs. A smoke bomb pointed into the system would likely work (might be easy to come by now with the 4th of july and all).

This is probably the not so great advice you were talking about, but just in case it happens to spark ideas on your end, I'll throw it out there :)

guido2

07-01-2010, 09:44 AM

Thanks again and any idea is good. I checked the shaft that drives impeller and good driving power there. Smoke sounds like a good idea and may try that sometime. In this case I have found the water escaping on the intake side of the pump at the anode.....seen in the photo. I didn't snap the picture while the water was running.....should have, but it comes out from under the anode where you see the slim opening. Why should unfiltered water be allowed to enter the system? Seems there is a problem inside the housing at or around the suction tube. The owner is hesitant to dismantle the outdrive but I may have to do that when he returns the rig after the 4th. Thanks Tim

guido2

07-03-2010, 11:16 AM

Any more imput would be welcome. Thanks, Tim

guido2

07-04-2010, 11:15 AM

Happy 4th everyone! Thanks for your advice. Tim

guido2

07-12-2010, 09:25 AM

Still no word on the boat, owner still has it out. If anyone else wants to review this case please advise......thanks, Tim

usmcdroach

07-12-2010, 09:57 PM

hey i got a 89 omc cobra 4.3 and have been fighting a overheating problem as well and just put clear hoses on the two out going tubes from thermo housing to exhaust and my left side has no flow im searching as to why but maybe you should see if you have water going both hoses if not maybe we can tackle this together

guido2

07-14-2010, 10:41 PM

The circulation systems are a bit different maybe but the same problem. In my case it has to be a delivery problem from outdrive pump. The customer used it all last week and no overheating unless he idles or trolls. He won't bring it back until the end of the season.......he is considering tackling the problem himself, but I have suspicion that it will continue to be an illusive problem. There has to be a leak on the suction side of the outdrive pump unit. I was about ready to crack the case but he needed the boat. I gave him the website here so he can review my research on it. My labor charges are pretty fair as I work at home, but I enjoy tackling those hard to solve problems. Others have worked on this rig with no solution. I won't tear something apart and charge a customer for my own mistake. By the same token I don't like to work for nothing. Thats why I research first, then try to fix it.

Ryanscolo

07-16-2010, 01:33 PM

damn... I have the complete opposite probels.....heats up at higher rpms....cools down at lower rpm's

guido2

07-17-2010, 09:55 AM

Ha! Maybe start a new thread, I'll watch it for any new ideas. Good luck!

usmcdroach

07-22-2010, 09:46 PM

ryanscolo thats the problem i was having i cleaned out the rust inside the manifolds where the water exits at i am going to test tomorrow or sat and i will let you know how it turns out

bow movement

04-02-2011, 10:22 AM

hey folks,

did anyone ever find any resolutions to this? I have a 1988 Bayliner Cierra Sunbridge 2455, with a "new" 5.7 OMC, cobra outdrive....SAME PROBLEM. This boat has cost me thousands, and I took it out last Friday, had no problems. Monitored cooling, oil pressure, etc the whole day, never missed a lick. Yesterday, my wife and I went to the marina to take it out, and being a new motor, I started it at dock while we loaded our cooler, fishing tackle, etc, and noticed it was getting warm. 10 hours later, I was still at dock, had hoses to tstat housing on and off a thousand times, removed outdrive impeller, etc, never could get it to pump water of any substantial amount. I did not try putting it into gear, as my boat is surrounded by other boats, and if I leave the dock, I better be "sure" because the vessels around me cost well in excess of $100k, dont want any accidents. I am suppose to meet the mechanic monday morning where he will tow me to loading ramp to take boat to his shop, but after reading this thread I cant help but wonder if in forward gear, my cooling problem will vanish as well? Any help you can give would be fantastic. This is motor #3 since I have owned this boat. First motor was junk when I got the boat, second motor was a salvage from donor boat, and now $4000 later its a "new" reman. motor. Really really dont want to put any more engines in this boat.

trilight

09-14-2011, 10:57 AM

I too have had the same problem. Sporadic waterflow coming from the outdrive. Very frustrating. I think I have solved it, since I have now been running for a week with good consistent water flow.
I have stinted the hose which connects the transom through pipe to the articulating outdrive by running a smaller diameter hose through it from the transom through pipe. Pushing my stint past the bends and a tighter obstruction in the original, possibly collapsed hose. I then cut off the stint at the transom through pipe, sewed dental floss through it, and tailed the dental floss over the through pipe, fastening it with the transom to tstat hose, [neccesary because the inner/stint hose wants to move out of the obstruction/collapsed hose with the water flow].

budman8

08-14-2012, 03:39 AM

Sorry guys, I'm a newbie and experiencing the same problem on our boat that we bought 3 weeks ago, everything was working fine until 2 days ago we took the boat out for a fishing trip but after running it for over 30 mins the engine starts to overheat wether idling or running speed, don't know where to start and ended up in this sites, very helpul and a lot of info. My question is can you service or remove the impeller if the boat is dock at the marina, we dont have a trailer to take it to a dry place, any suggestion, any help is greatly appreciated, thanks.

I too have had the same problem. Sporadic waterflow coming from the outdrive. Very frustrating. I think I have solved it, since I have now been running for a week with good consistent water flow.
I have stinted the hose which connects the transom through pipe to the articulating outdrive by running a smaller diameter hose through it from the transom through pipe. Pushing my stint past the bends and a tighter obstruction in the original, possibly collapsed hose. I then cut off the stint at the transom through pipe, sewed dental floss through it, and tailed the dental floss over the through pipe, fastening it with the transom to tstat hose, [neccesary because the inner/stint hose wants to move out of the obstruction/collapsed hose with the water flow].

o2batsea

08-14-2012, 10:35 AM

You have to remove the plastic cover to get to the impeller housing. Undo the cover bolts and remove the impeller. Lightly grease the new one with petroleum jelly and install with a slight twist. I start the twist at about 90 degrees to the left off from the keyway so that when it gets in there it will seat on the drive key properly. You'll see what I mean. If necessary, you can take the boat into shallow water and do it in your bare feet. OK to tilt the drive all the way up to ease access. Been there. Best to keep a spare impeller somewhere in your on board spares kit. In operation the impeller is water lubricated, so no need for tons of grease.

budman8

08-14-2012, 01:35 PM

o2batsea, thanks for your reply, we're going to take boat into a shallow water anh hopefully will be able to solve the overheating issue with this boat. Last night I read the reply over and over to familiarize myself with this unit. BTW what kind of material is this impeller made of and do they have a threaded part or a keyway that holds it in place into the shaft, thanks again.

You have to remove the plastic cover to get to the impeller housing. Undo the cover bolts and remove the impeller. Lightly grease the new one with petroleum jelly and install with a slight twist. I start the twist at about 90 degrees to the left off from the keyway so that when it gets in there it will seat on the drive key properly. You'll see what I mean. If necessary, you can take the boat into shallow water and do it in your bare feet. OK to tilt the drive all the way up to ease access. Been there. Best to keep a spare impeller somewhere in your on board spares kit. In operation the impeller is water lubricated, so no need for tons of grease.

o2batsea

08-15-2012, 08:31 AM

Impeller is either nitrile or butyl rubber. Not sure which. Probably butyl. It has a vee shaped keyway on the forward end of the impeller's hub. Only goes on one way, so it it's a go/no-go fit.

kim1349

08-16-2013, 03:04 PM

Stupid question. What is the purpose of the small vent hose? It was broken off the housing on this one and sprayed all over the place through the 3 bolted cover. Got a new housing with the fitting on it and will replace the hose but what is it's purpose?